The statements in this section are intended to provide background information related to the present disclosure and may not constitute prior art.
Many vehicles are powered by multi-cylinder, reciprocating piston, diesel engines which use a hydrocarbon fuel (or a bio-diesel fuel mixture) that, when mixed with air, is ignited during high compression of the air-fuel mixture in each cylinder. In the operation of diesel engines (and lean-burn gasoline engines) the mass ratio of air to fuel (e.g., 17:1 or greater) is well above the stoichiometric air-to-fuel ratio. A turbocharger may be used to deliver air into the intake manifold of the engine and fuel injectors are used to deliver controlled amounts of fuel to each cylinder. Many parameters of engine operation are controlled using a computer-based engine control module. The result of such well-managed delivery of fuel and excess air to each cylinder is that efficient usage of the fuel is attained. But the exhaust gas stream, combined from the exhaust of the respective cylinders in the exhaust manifold of the engine, contains significant amounts of carbon monoxide (CO), incompletely burned hydrocarbons (HC), mixtures of oxides of nitrogen (mainly NO, with some NO2, collectively NOx), and small particles of carbon, in addition to nitrogen, oxygen, carbon dioxide, and water.
Governmental regulations in the United States and other countries compel treatment of the exhaust streams from diesel engines on vehicles to reduce the quantity of each of CO, HC, NOx, and diesel particulates (micrometer size carbon particles) before the exhaust is discharged from the tailpipe of the vehicle. Thus, there is a need to design and place suitable reactors in the exhaust flow stream for conversion of these exhaust constituents to nitrogen, carbon dioxide and water before the treated exhaust is discharged from the exhaust system. Various catalyzed oxidation reactors and catalyzed reduction reactors are proposed for such exhaust treatment, and there is a corresponding need to assess the operation of such catalyzed reactors on each vehicle to determine whether they are functioning as required. There is a specific, government-mandated, need to determine whether a platinum-containing metal catalyzed DOC is functioning to suitably convert (oxidize) some nitrogen oxide, NO, to nitrogen dioxide, NO2, so that the exhaust gas composition will respond to a selective catalytic reduction reactor in converting NOx to N2 and water. The conversion of some NO to NO2 is important to removing NOx from the exhaust stream.